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ANNALS OF FAMILY MEDICINE ✦ WWW.ANNFAMMED.ORG ✦ VOL. 11, NO. 2 ✦ MARCH/APRIL 2013
116
ANNALS OF FAMILY MEDICINE ✦ WWW.ANNFAMMED.ORG ✦ VOL. 11, NO. 2 ✦ MARCH/APRIL 2013
116
Screening For Hypertension Annually Compared With Current Practice
ABSTRACTPURPOSE Hypertension is the most common diagnosis in ambulatory care, yet little evidence exists regarding recommended screening intervals or the sensitiv-ity and specifi city of a routine offi ce-based blood pressure measurement, the most common screening test. Screening for hypertension is usually performed by measuring blood pressure at every outpatient visit, which often results in tran-siently elevated fi ndings among adults who do not have a diagnosis of hyperten-sion. We hypothesize that a more limited annual screening strategy may increase specifi city while maintaining sensitivity.
METHODS A retrospective case-control study of 372 adults without hypertension and 68 patients with newly diagnosed hypertension was conducted to compare the usual screening practice of checking blood pressure at every visit with a sec-ond strategy that considered only annual blood pressure measurements.
RESULTS Specifi city improved from 70.4% (95% CI, 65.5%-75.0%) for the usual practice to 82.0% (95% CI, 77.7%-85.8%) for the annual screening strategy. No statistically signifi cant difference in sensitivity existed between the 2 methods.
CONCLUSION A limited annual screening strategy for hypertension can improve specifi city without sacrifi cing sensitivity when compared with routine screening at every visit in previously normotensive adults.
Ann Fam Med 2013;11:116-121. doi:10.1370/afm.1467.
INTRODUCTION
Hypertension is the most common diagnosis for which patients
seek ambulatory care in the United States, representing more
than 42 million visits in 2007.1 Yet there is little evidence to rec-
ommend a screening interval2 or to defi ne the sensitivity and specifi city
of the most common screening test, a routine offi ce-based blood pressure
measurement performed by manual sphygmomanometry. There is univer-
sal agreement among major national primary care organizations, including
The Joint National Committee on Prevention, Detection and Treatment of
Hypertension (JNC-7), the United States Preventative Service Task Force
(USPSTF), the American Academy of Family Physicians, and the Ameri-
can College of Physicians on the utility of screening for hypertension.2-4
JNC-7 recommends a 2-year screening interval for normotensive individu-
als (systolic blood pressure less than 120 mm Hg and diastolic blood pres-
sure less than 80 mm Hg) and a 1-year interval for individuals with prehy-
pertension (systolic blood pressure of 120-139 mm Hg or diastolic blood
pressure of 80-89 mm Hg), but it does not cite any references for these
recommendations.3 The USPSTF mentions the JNC-7 recommendations
regarding screening intervals but states, “the optimal interval for screening
adults for hypertension is not known.”2
Throughout the country, many primary care clinics routinely screen
for hypertension by checking blood pressures at every clinic encounter
regardless of the patient’s chief complaint, previous blood pressures, or
Gregory M. Garrison, MD, MS
Sara Oberhelman, MD
Department of Family Medicine, Mayo
Clinic, Rochester, Minnesota
Confl icts of interest: authors report none.
CORRESPONDING AUTHOR
Gregory M. Garrison, MD, MS
Department of Family Medicine
Mayo Clinic
200 First St SW
Rochester, MN 55905
ANNALS OF FAMILY MEDICINE ✦ WWW.ANNFAMMED.ORG ✦ VOL. 11, NO. 2 ✦ MARCH/APRIL 2013
117
HYPERTENSION SCREENING
the interval since the last blood pressure was obtained.
Even so, an estimated 30% of individuals with hyper-
tension are unaware they have the disease.3 According
to JNC-7, a diagnosis of hypertension requires “the
average of 2 or more properly measured, seated, blood
pressure readings on each of 2 or more offi ce visits.”3
It is well known that clinic blood pressures tend to be
higher than ambulatory blood pressures, the so-called
white coat effect.5-8 In addition, clinic blood pressures
are often not taken according to JNC-7 specifi cations,
leading to inaccurate and often elevated results.9,10
These factors, plus patient factors of acute pain, illness,
or anxiety, make interpreting clinic blood pressure val-
ues as a screening test for hypertension diffi cult.
With Americans making an average 3.2 medical
offi ce visits per year and the majority of these occur-
ring in primary care,1,12 there is ample opportunity to
design a better, more limited screening strategy for
hypertension that meets JNC-7’s recommendations.3
This pilot study compares the current clinical prac-
tice of screening for hypertension by checking every
patient’s blood pressure at every visit vs a more limited
strategy that screens for hypertension annually.
METHODSWe compared 2 screening strategies for low-risk
patients. The fi rst strategy is the usual clinical practice
of measuring a patient’s blood pressure at every visit.
Because we hypothesized that a limited annual screen-
ing strategy would increase specifi city while main-
taining sensitivity, we simulated a second strategy by
considering blood pressures obtained only at general
medical examination visits and any other visit when it
had been more than 1 year since the last blood pres-
sure measurement was obtained (Figure 1).
To compare the screening strategies, we conducted
a retrospective study for the 5 years preceding August
1, 2010. Subjects were family medicine patients at
Mayo Clinic Rochester who were aged 18 to 75 years
at the start of the study period, were not pregnant,
remained active patients for the entire 5 years, and
had at least 1 offi ce blood pressure recorded during
the study period. We excluded patients with type 1
or 2 diabetes, coronary artery disease, or stage 3 or 4
chronic kidney disease because of the differing stan-
dards for treatment of blood pressure in these indi-
viduals. Additionally, because of the effect on blood
pressure, we excluded patients taking any antihyper-
tensive medications for migraine prophylaxis, periph-
eral edema, or other reasons at any point during the
study period before a diagnosis of hypertension. All
patients had signed a research authorization allowing
retrospective review of their electronic medical record.
The study was reviewed and approved by our Institu-
tional Review Board.
We used an administrative database containing
International Classifi cation of Disease (ICD-9) billing codes
for the past 16 years to construct pools of patients with
hypertension diagnosed during the study period and
patients who did not have hypertension based on the
inclusion and exclusion criteria defi ned previously. We
looked for patients never having an ICD-9 code 401.x
(hypertension) before the start of the study and who
were subsequently given an ICD-9 code 401.x during
the study period, as well as patients who never had an
ICD-9 code 401.x.
We randomly selected 236 patients who received a
diagnosis of hypertension during the study period and
500 normotensive patients using the SAS procedure
survey select (SAS 9.2 , SAS Institute Inc). We screened
for antihypertensive medication use with a computer-
ized text-matching algorithm, and the investigators
conducted a manual chart review of all patients.
We entered data from all study patients regarding
blood pressure values at various outpatient visits, medi-
cations, and demographics into a relational database
(PostgreSQL 8.3, PostSQL Global Development Group,
running on Mac OS 10.7.3). The great majority of blood
pressure measurements were obtained by a licensed
practical nurse using a calibrated aneroid device.
Statistical analysis was carried out using R 2.15.0
statistical software (http://cran.r-project.org/src/base/R-
2/R-2.15.0.tar.gz ) running on Mac OS 10.7.3. Patients
with diagnosed hypertension and patients in the group
Figure 1. Proposed limited annual screening algorithm for hypertension.
BP = blood pressure; CAD = coronary artery disease; CKD = chronic kidney disease; DM = diabetes mellitus; HTN = hypertension.
Low-Risk Patient
Age >18 y; no DM, CAD, CKD, HTN; not pregnant; not on anti-
hypertensive medication
Health maintenance visit?
Last BP >1 y Ago
Record screening BPNo BP screening necessary
No Yes
No Yes
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HYPERTENSION SCREENING
with no hypertension were compared using Fisher’s
exact test for categorical data and t tests for numeri-
cal data. P values of less than .05 were considered
signifi cant. Sensitivity and specifi city, including 95%
confi dence intervals, were calculated for each screening
strategy using the patient as the unit of analysis. Any
blood pressure of 140 mm Hg systolic or 90 mm Hg
diastolic or greater was considered a positive screen-
ing test. A physician’s diagnosis of hypertension was
considered the reference standard for positive disease.
Assuming a sensitivity of 95% and a specifi city of 75%,
with desired 95% confi dence intervals of 5%, it was
estimated 73 patients with diagnosed hypertension and
288 patients without hypertension would be needed.
RESULTSAs is typical for administrative or billing databases,13,14
there were substantial differences from the actual
clinical notes among the 236 potential patients with
hypertension diagnosed during
the study period and the 500
potential patients without hyper-
tension. For instance, 43 patients
in the hypertension group had a
diagnosis of elevated blood pres-
sure without hypertension that
was mistakenly coded as ICD-9
code 401.x; 34 patients never had
a diagnosis of hypertension but
mistakenly were given an ICD-9
401.x billing code, often during a
procedure or hospitalization; and
12 patients in the hypertension
group and 4 patients in the group
with no hypertension were found
to have a clinical diagnosis of
hypertension before the start of
the study that was not recorded
as a ICD-9 401.x billing code in
the administrative database (Fig-
ure 2).
After elimination of the mis-
coded patients, we analyzed data
from 68 patients with hyperten-
sion diagnosed during the 5-year
study period and 372 patients
with no hypertension during the
same period. These 440 patients
had 4,287 blood pressures
recorded. Sex and smoking sta-
tus did not differ between those
with hypertension and those with
no hypertension. The number
of visits per patient per year was also similar, with the
patients with hypertension averaging 2.5 (SD = 2.8)
visits per year and the patients with no hyperten-
sion averaging 1.9 (SD = 1.3) visits per year (P = .096).
Patients with hypertension were older than patients
with no hypertension (47.6 years, SD = 10.4 years
vs 41.2 years, SD = 12.7 years, respectively; P <.001)
and heavier (body mass index 33.6 kg/m2, SD = 6.8 vs
28.6 kg/m2, SD = 8.7 kg/m2, respectively; P <.001). As
expected, average blood pressures were higher in the
patients with hypertension than the patients with no
hypertension. Table 1 summarizes these results.
The screening strategy of checking blood pressures
at every visit identifi ed all 68 patients with hypertension
diagnosed during the study period who had at least 1
positive screening blood pressure higher than 140/90
mm Hg, consistent with the criteria for diagnosis. There
were, however, 110 (29.6%) patients in the group with
no hypertension who were found to have at least 1
blood pressure measurement higher than 140/90 mm Hg
Figure 2. Case and control selection.
BP = blood pressure; CAD = coronary artery disease; CKD = chronic kidney disease; DM = diabetes mellitus; HTN = hypertension.
Patients With Diagnosed
Hypertension
Patients With No
Hypertension
Antihypertensive medication
Manual Chart Review
77 32
43
412
34
2 92
68 372
Elevated BP without HTN
No HTN
Exclusion criteria met
Age >18
CAD/DM/CKD
Pregnancy
No BPs recorded
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119
HYPERTENSION SCREENING
during the study period. In fact,
266 of 3,299 (8.1%, 95% CI, 7.2%-
9.0%) blood pressures obtained in
this group were at or higher than
140/90 mm Hg. Usual practice, as
expected, had identifi ed 100% of
patients with diagnosed hyperten-
sion (sensitivity 100%, 95% CI,
92.2%-100%), with a specifi city of
70.4% (95% CI, 65.5%-75.0%).
The annual screening strategy
retained 39.3% (1,686) of the
4,287 blood pressures obtained
during the study period. This
method found the same rate of
elevated blood pressures among
the retained readings from
patients with no hypertension,
with 106 of 1,373 (7.7%, 95%
CI, 6.4%-9.3%; P = .692) with
blood pressures at or higher than
140/90 mm Hg. Screening less
frequently resulted in only 67
patients in the group (18.0%)
with no hypertension having
elevated blood pressures. The
annual screening strategy failed,
however, to identify 5 (7.4%)
patients with hypertension on or
before the date of their original
diagnosis. This method yielded
a sensitivity of 92.6% (95% CI,
83.7%-97.6%) and a specifi city of
82.0% (95% CI, 77.7%-85.8%).
Table 2 contrasts the results
obtained by both methods.
DISCUSSIONHypertension screening is an
important part of preventive
health care delivered by primary
care physicians. It is essential to
understand the implications of a screening test’s char-
acteristics to interpret results and design a screening
strategy effectively. This initial pilot study proposes an
annual screening strategy for hypertension using the
most common screening test, the offi ce-based manual
blood pressure measurement, which improves specifi c-
ity while maintaining sensitivity.
SensitivityAn objective of any screening strategy is to classify cor-
rectly those individuals with hypertension. Sensitivity
describes a test’s ability to classify correctly those with
disease (Table 3). With a highly sensitive test, the false-
negative or type 2 error rate is negligible. Thus, a nega-
tive result tends to rule out the possibility of disease.15
As expected, the baseline practice of checking
blood pressure at every visit yielded 100% sensitiv-
ity. The proposed annual screening strategy failed to
identify 7.4% of newly hypertensive patients as quickly
as the baseline strategy. This difference was not signifi -
cant, as the 95% confi dence intervals overlapped. Given
the slowly progressive nature of morbidity resulting
Table 1. Demographic Information on Patients With Diagnosed Hypertension and Patients With No Hypertension
CharacteristicHypertension
(n = 68)No Hypertension
(n = 372) P Value
Sex, No. (%) >.999Male 33 (48.5) 179 (48.1)Female 35 (51.5) 193 (51.9)
Age, year (SD) 47.6 (10.4) 41.2 (12.7) <.001
BMI, kg/m2 (SD) 33.6 (6.8) 28.6 (8.7) <.001
Smoking status, No. (%) .530
Never 28 (66.7) 83 (58.9)
Quit 11 (26.2) 40 (28.3)
Current 3 (7.1) 18 (12.8)
Visits per year, No. (SD) 2.5 (2.8) 1.9 (1.3) .096
Average blood pressure
Systolic, mm Hg (SD) 135.3 (11.1) 114.7 (11.4) <.001
Diastolic, mm Hg (SD) 82.7 (6.7) 70.1 (7.5) <.001
BMI = body mass index.
Table 3. A 2 x 2 Table for Screening Tests for Hypertension
Elevated Screening Blood Pressure Yes No
Yes True positive False positive (type I error)
No False negative (type II error) True negative
SensitivitySn =
TP
TP + FNSp =
TN
TN + FP
Table 2. Sensitivity and Specifi city of Blood Pressure Screening Strategies
Strategy
Hypertension Sensitivity, % (95% CI)
Specifi city, % (95% CI)Yes (Cases) No (Controls)
Typical practice (all visits)
Positive 68 110 100 (92.2-100)
70.4 (65.5-75.0)
Negative 0 262
Limited strategy (annual screening)Positive 63 67 92.6
(83.7-97.6)82.0
(77.7-85.8)Negative 5 305
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HYPERTENSION SCREENING
from hypertension,16 whether this delay in diagnosis is
clinically relevant is debatable. In this study, we could
not consider visits that occurred after a diagnosis of
hypertension was made, as treatment would affect
these blood pressure values. Thus it was impossible to
ascertain whether and when these patients would have
had hypertension diagnosed using the proposed annual
screening strategy. Considering that hypertensive
patients had an average of 2.5 visits per year, the delay
is unlikely to be more than a few months.
Specifi citySpecifi city describes a test’s ability to correctly classify
those without disease (Table 3). With a highly specifi c
test the false-positive or type I error rate is minimal.
A positive result therefore rules in a disease.15 If large
numbers of disease-free individuals are screened
repeatedly, then even highly specifi c tests can generate
unwieldy numbers of false-positive results, for which
patients must undergo further testing.
This study found that the baseline practice of
screening for hypertension by checking blood pres-
sures at every offi ce visit has a poor sensitivity of
70.4%. During the 5-year study period, 29.6% of
adults who never had hypertension diagnosed had at
least 1 elevated blood pressure reading. These ele-
vated readings can lead to follow-up visits, laboratory
testing, and patient anxiety, or as in “The Shepherd’s
Boy and the Wolf,”11 they can lull the physician into a
sense of complacency, delaying the diagnosis of actual
hypertension.
One way to compensate for a screening test’s poor
specifi city is to target a limited population for screen-
ing; however, JNC-7 recommendations clearly indicate
the need to screen all adults for hypertension.3
In slowly progressive diseases, another way to
compensate for poor specifi city is to reduce the fre-
quency of screening.17 Obviously, clinical consider-
ations come into play as the screening needs to occur
frequently enough to detect the disease in its earliest
stages, when it is easily treated and before morbidity
develops. Mild to moderate hypertension is a slowly
progressive chronic disease that causes complications
and target organ damage over the course of years.16
Given a test with high sensitivity but poor specifi city,
such as offi ce blood pressure screening, performing it
too frequently increases false-positive results but does
not improve disease detection.
Less frequent screening is the tactic applied by
our proposed annual screening strategy. It reduced
the number of screenings performed by 60.7%. The
reduced frequency of screening produced a signifi cant
decrease in the false-positive rate from 29.6% to 18.0%
of nonhypertensive adult patients over a 5-year period.
Applied to the roughly 2,000 healthy adults cared for
by a typical family physician, it results in 232 fewer
patients needing further workup over 5 years.
Reducing the number of unnecessary blood pres-
sures screenings in healthy adults provides benefi ts
in addition to improving the false-positive rate. It can
increase clinic effi ciency, reduce clerical burdens, and
focus attention on accurately obtaining screening
blood pressure measurements. JNC-7 specifi es that an
accurate blood pressure measurement should be the
mean of 2 auscultatory readings taken with an appro-
priately sized cuff with the patients’ feet on the fl oor
and arm supported at heart height after being seated
quietly in a chair for 5 minutes.3 In the typical busy
family medicine clinic with 15-minute appointments,
there is no time for this method for every patient at
every visit.6,18 Instead, patients are all too often rushed
down the hallway from a waiting room, and a blood
pressure is immediately measured. Reducing the fre-
quency of screening blood pressures may allow clinical
staff time to measure blood pressures more accurately.
For instance, oscillometric devices, such as the BpTRU
(BpTRU Medical Devices), that take multiple readings
over several minutes may be used.19
LimitationsIdentifying patients with newly diagnosed hyperten-
sion by ICD-9 codes proved problematic. Manual chart
review revealed substantial inaccuracies leading to
fewer patients than originally forecast, which limited
the study’s ability to detect differences in sensitivity
between the 2 methods. The fewer patients did not
affect the study’s primary aim of detecting differences
in specifi city, however.
Determining a group of patients with no hyperten-
sion was also problematic. This study used a 5-year
time frame to look for the development of hyperten-
sion, and thus we do not know what happens in the
future to patients who did not have hypertension
diagnosed but who had elevated blood pressures. Do
they go on later in life to develop hypertension? Addi-
tionally, we did not design our study to examine the
effect that our proposed screening strategy might have
on morbidity from hypertension. Further studies with
longer time frames and other endpoints are required to
answer these questions.
The proposed annual screening for hypertension (in
line with selection criteria for blood pressure measure-
ments in this analysis) would entail measuring blood
pressure for each patient at all preventive care visits or
if it had been at least 1 year since the last blood pres-
sure measurement. This simplistic approach makes the
algorithm easy to understand and implement, but it
may overlook other important clinical factors.
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HYPERTENSION SCREENING
Age and body mass index are well-established risk
factors for hypertension,20,21 and the observed differ-
ences between patients with diagnosed hypertension
and patients with no hypertension are not surprising.
Such differences did not affect our sensitivity and
specifi city analysis.
The choice of a physician diagnosis of hypertension
as the reference standard for disease may underestimate
its prevalence in the study population.3 JNC-7 provides
a defi nition for hypertension as “the average of 2 or
more properly measured, seated blood pressure read-
ings on each of 2 or more offi ce visits.”3 Unfortunately,
very few routinely obtained, offi ce-based blood pressure
measurements meet the requirements of this defi ni-
tion.9,10 Thus using the JNC-7 defi nition as the reference
standard for hypertension in this study was impracti-
cal, as there was no guarantee that the retrospectively
obtained blood pressures met the rigorous requirements.
Although a limitation, it is not necessarily a weakness,
because the purpose of this study was to investigate the
screening utility of routinely obtained typical offi ce-
based blood pressure measurements, which do not
always meet the strict JNC-7 requirements.
Finally, there is a distinction between obtaining a
blood pressure reading for hypertension screening pur-
poses and obtaining a blood pressure reading because it
is clinically relevant. There are many clinical scenarios,
such as chest pain, palpitations, lightheadedness, and
severe infections, where obtaining a blood pressure mea-
surement is necessary to guide diagnosis and treatment
decisions, but the purpose is not to screen for hyperten-
sion. This study does not suggest that these blood pres-
sures should not be obtained; only that they should be
interpreted cautiously when diagnosing hypertension.
To read or post commentaries in response to this article, see it online at http://www.annfammed.org/content/11/2/116.
Submitted March 13, 2012; submitted, revised, July 28, 2012; accepted August 21, 2012.
Key words: hypertension; blood pressure; blood pressure determi-nation; preventive health services; sensitivity and specifi city; mass screening
Funding support: Funding was provided by Mayo Clinic Department of Family Medicine.
Acknowledgments: We would like to thank Melissa Gregg and Julie Maxson for their assistance with data collection. Without their expertise, this study would not have been possible.
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